In general I am interested in the regulatory mechanisms which control the different functional levels of the microcirculation in normal and altered physiological and pathological states. This particular project will study microvascular control in skeletal muscle and alterations in this control which occur with exercise training and hypertension. The rat cremaster muscle will be used as the experimental model. Specifically, I will examine the hypothesis that changes in local PO2, PCO2 and pH can significantly influence the microcirculation by altering vascular smooth muscle sensitivity to norepinephrine. In addition, this project will test the hypothesis that exercise training in the normotensive animal will increase the microcirculatory response to alterations in PO2, PCO2 and pH, and thus, decrease small vessel sensitivity to norepinephrine. Finally, I will evaluate the hypotheses that PO2, PCO2 and pH have a significant effect on vascular sensitivity in the spontaneously hypertensive rat, but not in the renovascular hypertensive rat, and that exercise training will decrease vascular sensitivity to norepinephrine and resting blood pressure in the spontaneously hypertensive rat, but will have no effect in the renovascular hypertensive rat. This research program will utilize closed-circuit television microscopy for direct in vivo measurements of the diameters of small arteries, small veins, arterioles and venules in the rat cremaster muscle. My microcirculatory preparation encompasses the advantages of in vivo studies (intact blood and nerve supply) and those of in vitro studies (fine control of tissue pH, PO2, PCO2, temperatures, ion concentration, drug concentrations, etc.). Concentration-response curves will be determined under different tissue conditions for topical application of norepinephrine in normotensive, spontaneously hypertensive and renovascular hypertensive rats. Each group of rats will be subdivided into those which have exercised (swimming 1hr/day for six weeks) and those which have not exercised.